A Study On Microleakage Of Class â…¡ Composite Restorations

Light-cured resin composites are widely used in clinical practice because of many advantages, such as esthetic looking, no population and improved bonding to tooth structure. It has a tendency to replace silver amalgam in the future. Researchers keep on studying and exploring in order to improving the properties of composite resins, and the problem of volumetric shrinkage of composite resins during polymerization become the major object.Polymerization shrinkage is one of the common problem among composite resins, which has been considered as the main reason of the marginal microleakage in composite restorations. In some circumstance, microleakage becomes a source of postoperative sensitivity, marginal stain, secondary caries and eventual failure of the restorations. All of these can affect clinical effect directly. Polymerization shrinkage are caused by two main factors: the nature of composite resins and clinical filling procedure. The former includes organic matrix, filler contents, elastic modulus, flow ability, etc. The latter includes cavity type, base material, curing mode, etc. Class II cavity has been considered as a challenge for composite restorations due to the difficulty to control the gingival microleakage, especially when gingival margins placed in cemetum/dentin. The purposes of this study were to evaluate the effect of the type of composite resins and different treatments on microleakage of class II composite restorations in vitro, and estimate the clinical effect of composite restorations in vivo.Part I Microleakage of class II composite restorations: in vitro studyExperiment one: Effect of different methacrylate resin composites on microleakage of class II composite restorations[Materials and Methods] Class II slot cavity was prepared on mesio-occlusal surface in each of 30 freshly extracted human molars. Teeth were randomly divided into 3 groups and were filled with 3 types of resin composites respectively: packable resin composite(P60), hybrid resin composite(Z250) and nanofilled resin composite(Z350). After thermocycling, all teeth were immersed in basic fuchsine solution. Each sample was then sectioned longitudinally into 3 pieces in a mesio-distal direction. Dye penetrations were examined under stereomicroscope.[RESULTS] No significant differences (P>0.05) were found among 3 composite resins.[CONCLUSION] In this study the resin composites types have no effect on gingival microleakage of class II cavities with cementum/dentin margins.Experiment two: Effect of composites with different types of resin on microleakage of class II composite restorations[Materials and Methods] Class II slot cavity was prepared on mesio-occlusal surface in each of 20 freshly extracted human molars. Teeth were randomly divided into 2 groups and were filled with novel silorane-based composite P90 and conventional methacrylate resin composite P60 respectively. After thermocycling, all teeth were immersed in basic fuchsine solution. Each sample was then sectioned longitudinally into 3 pieces in a mesio-distal direction. Dye penetrations were examined under stereomicroscope.[Results] The samples filled with P90 showed significantly lower gingival microleakage than the ones filled with P60 (P<0.05).[Conclusion] It could be concluded that silorane-based composite reduce gingival microleakage of class II cavities with cementum/dentin margins.Experiment three: Effect of preheating composites on microleakage of class II composite restorations[Materials and Methods] Class II slot cavity was prepared on mesio-occlusal surface in each of 20 freshly extracted human molars. Teeth were randomly divided into 2 groups and were filled with packable resin composite P60 which was preheated to 45oC in constant temperature cabinet and was not preheated at room temperature (16oC) respectively. After thermocycling, all teeth were immersed in basic fuchsine solution. Each sample was then sectioned longitudinally into 3 pieces in a mesio-distal direction. Dye penetrations were examined under stereomicroscope.[Results] The samples filled with preheated composites showed significantly lower gingival microleakage than the ones unpreheated (P<0.05).[Conclusion] It could be concluded that preheated composites reduce gingival microleakage of class II cavities with cementum/dentin margins. Partâ…¡The evaluation of clinical application of composite resins in the initial stage[Materials and Methods] 117 teeth with dental defect were admitted for composite restorations. Then the composite restorations were evaluated by modified USPHS criteria after one year.[Results] 2 failures were recorded among the 106 restorations and 4 teeth were affected by slightly marginal stain. The clinical effect of composite restorations after one year was acceptable.[Conclusion] The short-term clinical effect of composite restorations was satisfactory.